1. Field of the Invention
This invention relates to information recording apparatus and an information retrieval or reproducing apparatus in which information such as a video signal, audio signal or computer data signal can be recorded in high packing density on many tracks formed on a rotary recording medium, and any desired information can be easily read or reproduced from the corresponding track on the recording medium. This invention relates also to such an information recording medium. More particularly, this invention relates to apparatus of the kind above described in which information such as a video signal, audio signal or computer data signal is converted into a binary signal form to be recorded by recording means in a high packing density in the form of an irregular pattern of projection and depression or light and shade on a rotary recording medium or disc without any mechanical contact with the recording medium, and any desired information can be accurately reproduced by reproducing means without any mechanical contact with the recording medium, for example, by use of a radiation beam such as an optical beam.
2. Description of the Prior Art
In a reproducing apparatus of the kind above described, it is necessary to detect an information track having desired information recorded thereon from among many information tracks carrying various information recorded in high packing density and to shift a reproducing beam spot to the detected track position so that the desired information can solely be accurately retrieved for reproduction.
Philips Technical Review, Vol. 33, 1973, No. 7 describes in detail a method of information retrieval from a recording disc having information recorded on information tracks extending a spiral form from the outer peripheral edge toward the center of the disc. The method disclosed in this publication comprises the steps of drawing for locating a reproducing beam spot on one of the information tracks adjacent to the outer peripheral edge of the disc, shifting the beam spot in the radial direction of the disc while crrying out tracks control to prevent the beam spot from escaping from the information track, reproducing the information recorded on this information track, comparing the reproduced information with desired information to detect coincidence therebetween, and after detecting the information track on which the desired information is recorded, shifting the beam spot to the desired information track. However, this method is defective in that a great length of time is required until the desired information track is detected.